Align crud uploads with Dart implementation

[simolus3]

The Dart SDK invokes the CRUD upload method of the configured backend connector at least once per connect() call, even if we can't connect to the streaming sync endpoint. We want the same behavior in the JS SDK, and this PR adds that.

To make the implementation easier to reason about, this also aligns the implementation with the Dart SDK:

• We call crudUploadLoop in connect(), it takes a scoped abort signal now to abort along with the corresponding streamingSync() call after a disconnect.
• Instead of invoking uploads directly in an event handler, we create something resembling a stream controller to dispatch and throttle events on the consuming side.

Note that there are still some fishy things going on here, e.g. we break out of the _uploadAllCrud() loop if there's an error and we're not connected. The Dart SDK does the same, and this PR is still an improvement, but we should probably spec out how we actually want the upload flow to behave before applying this to other SDKs.

[changeset-bot]

🦋 Changeset detected

Latest commit: 1cffb2e

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 7 packages

Name	Type
@powersync/common	Patch
@powersync/node	Patch
@powersync/op-sqlite	Patch
@powersync/react-native	Patch
@powersync/tanstack-react-query	Patch
@powersync/web	Patch
@powersync/diagnostics-app	Patch

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[simolus3]

It looks like the Tauri integration tests are broken (timeouts without a message). They pass locally though, so I'll merge this and investigate those failures on another branch.